tty: serial: fsl_lpuart: use UARTCTRL_TXINV to send break instead of UARTCTRL_SBK
commit 2474e054 upstream. LPUART IP now has two known bugs, one is that CTS has higher priority than the break signal, which causes the break signal sending through UARTCTRL_SBK may impacted by the CTS input if the HW flow control is enabled. It exists on all platforms we support in this driver. So we add a workaround patch for this issue: commit c4c81db5 ("tty: serial: fsl_lpuart: disable the CTS when send break signal"). Another IP bug is i.MX8QM LPUART may have an additional break character being sent after SBK was cleared. It may need to add some delay between clearing SBK and re-enabling CTS to ensure that the SBK latch are completely cleared. But we found that during the delay period before CTS is enabled, there is still a risk that Bluetooth data in TX FIFO may be sent out during this period because of break off and CTS disabled(even if BT sets CTS line deasserted, data is still sent to BT). Due to this risk, we have to drop the CTS-disabling workaround for SBK bugs, use TXINV seems to be a better way to replace SBK feature and avoid above risk. Also need to disable the transmitter to prevent any data from being sent out during break, then invert the TX line to send break. Then disable the TXINV when turn off break and re-enable transmitter. Fixes: c4c81db5 ("tty: serial: fsl_lpuart: disable the CTS when send break signal") Cc: stable <stable@kernel.org> Signed-off-by:Sherry Sun <sherry.sun@nxp.com> Link: https://lore.kernel.org/r/20230519094751.28948-1-sherry.sun@nxp.com Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
parent
ae7fb0c8
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